As well known by those skilled in the art, chromatographic systems rely on the use of valves to allow reproducible sample introduction and various column switching schemes.
Diaphragm valves of various designs are known in the art for chromatography applications. Such diaphragm valves have been used in many commercially available gas chromatographs. They are apt to be integrated more easily in a gas chromatograph due to their physical size and since the actuator is embedded in the valve itself. These characteristics make them attractive for gas chromatograph manufacturers.
For example, international application No. PCT/CA2008/002138, filed Dec. 5, 2008 by the present applicant and published as WO2009/073966, as well as international application no. PCT/CA2009/001783, also by the present applicant, and published as WO2010/063125, disclose such a diaphragm-sealed valve. In addition, U.S. Pat. Nos. 7,216,528 and 7,503,203 issued to the present applicants on May 15, 2007 and Mar. 17, 2009, respectively, disclose other variants of diaphragm-sealed valves.
Referring to FIG. 1 (PRIOR ART), there is shown an example of a typical diaphragm-sealed valve as known in the art. The valve 1 is provided with a top block 2 having an interface 4 and a plurality of ports 6. Each one of the ports 6 opens at the interface 4 and has a thread passage 8 to connect various analytical fitting and tubing (not shown). At the bottom of the thread passage 8, there is a conduit 10 extending in the top block 2 and opening into ports 6 at the interface 4. The ports 6 are arranged along a line, such as, for example, a circular line, on the interface 4 of the top block 2. The interface 4 is advantageously flat and polished to minimize leaks between ports 6 and from the ambient atmosphere. The valve 1 is also provided with a bottom block 12 and a diaphragm 14, which is generally made of material such as polyimide, Teflon™ (polytetrafluoroethylene) or other polymers. The diaphragm 14 is positioned between the top block interface 4 and the bottom block 12, and has a recess 18 therein extending along a line formed by the ports 6 and biased away from the interface 4 of the top block 2. The recess 18 in the diaphragm 14 sits in a matching recess 20 made in the bottom block 12, thereby allowing some clearance for fluid circulation between adjacent ports 6.
The valve 1 is also provided with a plurality of plungers 16 mounted in the bottom block 12, each being respectively arranged to be able to compress the diaphragm 14 against the top block 2 at a position located between two of the ports 6. Preferably and as illustrated, in the case of a 6 port valve, when the valve is at rest, three plungers 16 are up while the other three are down. When the plungers are up, they compress the diaphragm 14 against the top block 2 and close the conduits made by the diaphragm recess 18, so that fluid circulation is blocked. The bottom block 12 keeps the plungers 16 and the actuation system in position.
It is common to designate a portion of the plungers 16 as “normally open” and another portion as “normally closed”. A normally open plunger 16 is biased downwards, i.e. away from the diaphragm 14, and therefore normally allows fluid circulation between the two adjacent ports 6. A normally closed plunger 16 is biased upwards, i.e. towards the diaphragm 14, and therefore blocks fluid circulation between the two adjacent ports 6. A user may actuate the valve 1 in order to alter the positions of the plungers 16, for example by sliding upwards and downwards the normally open and closed plungers 16, respectively.
It has been found that for the valve to be effective in a number of applications, the components of the actuation system of the valve must be machined with a high level of mechanical tolerance and special procedures are required during assembly and testing. For example, plungers must be sorted by their length, to make sure that inside any valve, plungers have the exact same length. Moreover, extra care must be shown to ensure that plungers are aligned and centered in the plunger passages of the cylinder body and remain centered over time. Indeed, friction will eventually generate wear and resulting particles that will build up and affect valve performances, therefore, special dowel pins and precise alignment marks are often necessary. The precise assembly of the component requires skilled assembly technicians and makes the assembly process long and costly.
In view of the above, there is a need for an improved valve which, by virtue of its design and components, would be able to overcome or at least minimize some of the above-discussed prior art concerns.